Wood golf club head

ABSTRACT

A wood club head includes: a face portion; and a sole portion, wherein: a distance between a point of intersection where a perpendicular which passes through the position of the center of gravity of the club head intersects a horizontal line which passes through a leading edge in such a state that a sole of the club head sits flat properly and the leading edge, that is, a depth of the center of gravity VZG is defined as below: VZG&lt;0.7159×(loft angle)+11.78; and VZG&gt;face maximum height×tan(loft angle); a surface shape of the face portion is formed into a cylindrical curved surface having only a bulge radius; and a depth of the club head from the leading edge to back end is 60 mm or more.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wood golf club head which is referred to as a fairway wood for striking directly a ball sitting on grass.

2. Description of the Related Art

One of characteristics of a wood golf club head is that the center of gravity lies deep in the club head. Although there are drawbacks in relation to the deep center of gravity, it has conventionally been well accepted that it is good that the center of gravity is deep and low, as disclosed in JP-A-2001-212272. A drawback in relation to the deep center of gravity will be described by reference to FIG. 5. In the figure, a sweet spot SS lies at a point on a face where a perpendicular drawn from the center of gravity G meets the face. Many centers of gravity G shown in FIG. 5 represent actual positions of centers of gravity of 23 commercially available fairway woods. In order to hit a ball far, it is ideal to hit the ball in the vicinity of the sweet spot SS. With the fairway wood used for striking a ball B on the grass, however, it is a reality that the striking point of the ball B lies far below the sweet spot SS even though a most ideal impact is realized. A point which is referred to, herein, as the “most ideal impact gravity becomes more serious.

SUMMARY OF THE INVENTION

A trajectory of a ball launched by a powerful golfer with such a golf club according to a related art results in something like a trajectory in which the ball is blown up in spite of the roll radius designed on the surface of the face of the club head. However, with senior golfers and female golfers, it can be said that there is seen no such trajectory in which the ball is blown up. The power is required to draw the trajectory in which the ball is blown up, and the senior golfers and female golfers are feeling it necessary to blow up their trajectories further, although they are concerned about their low ball trajectories.

When studying about causes for the low ball trajectory, firstly, it is raised that the ball is hit at an off-spot on the club head. FIG. 6 is a diagram corresponding to FIG. 5 and shows as the results of the study that the spots and the striking points lie largely apart from each other at each loft angle. For example, in a 5-wood of a loft angle of 25 degrees which many female golfers are likely to use, the ball is understood to be hit at a point on the club head which is apart 14 mm from the sweet spot. It is obvious from the same figure that the distance between the striking point and the sweet spot increases as the loft angle increases, and considering a future tendency that there will more and more senior golfers and female golfers point” is a striking point of a ball sitting on the ground or grass when striking the ball with a wood club and is considered to be situated on average in the position of the height of a point where the surface of a face of a wood golf club head which is placed in an address posture at proper loft angle (θ) and lie angle with a sole surface thereof in contact with the same ground as that where the ball sits, that is, the height of a geometrical contact point which will be expressed by the following expression or in the vicinity of a point therebelow.

Geometrical contact point height=(ball radius)×(1−sin θ)

Furthermore, since the center of gravity G is deep, a back spin which is equal to or larger than the loft angle is generated to thereby decrease the flight of the ball. In the related art, the high trajectory due to the excessive spin is dealt with by designing the roll radius on the surface of the face.

Conventionally, the wood golf club head is formed by persimmon or stainless including a hollow portion. Recently, according to the advance in technology, a wood golf club head is formed by titanium alloy including a hollow portion. As the result, a club head for a fairway wood grows in size, and the volume of the recent club head becomes about 140 to 180 cc. According to the growing in size of the recent club head, the center of gravity becomes deeper than that of the conventional club head, and drawbacks in relation to the deep center of who use clubs whose loft angles are larger than that of the 5-wood, this off-spot distance needs to be reduced. Secondly, there exists a drawback in relation to the roll radius on the surface of the face of the club head. In most of the fairway woods in which a ball is hit at a point lying below the center of the surface of the face, a real loft angle of the striking point becomes smaller than a nominal loft angle set by the manufacturer due to the roll radius, whereby the launch angle becomes lower and the back spin is reduced. Because of this, the senior golfers and female golfers have to face the reality that they have more difficulty in hitting a ball into a higher trajectory.

The invention is made in view of these situations and an object thereof is to provide a wood golf club head with which in particular, an average golfers, the senior golfers and female golfers also find it easy to hit a ball into a higher trajectory.

With a view to attaining the object, according to the invention, there is provided a wood club head including: a face portion; and a sole portion, wherein: a distance between a point of intersection where a perpendicular which passes through the position of the center of gravity of the club head intersects a horizontal line which passes through a leading edge in such a state that a sole of the club head sits flat properly and the leading edge, that is, a depth of the center of gravity VZG is defined as below: VZG<0.7159×(loft angle)+11.78; and VZG>face maximum height×tan(loft angle); a surface shape of the face portion is formed into a cylindrical curved surface having only a bulge radius; and a width of the club head from the leading edge to the back end is 60 mm or more.

According to the invention, the VGZ becomes shallow, the height of the center of gravity laying at a higher location on the surface of the face is lowered, and the off-center amount is reduced, whereby hitting at the points off the center is reduced. In addition, the roll design is discarded and the surface of the face of the club head is formed into the cylindrical curved surface having only the bulge radius, whereby balls can easily be hit into a higher trajectory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a design method of the invention;

FIG. 2 is a graph showing the results of a study of the current state of the depth of the center of gravity (VZG);

FIG. 3 is a drawing illustrating an improving method of a club head according to a related art;

FIG. 4 is a drawing illustrating the effect resulting when the face surface is modified to one having only a bulge radius;

FIG. 5 is a drawing illustrating a drawback of the club head according to the related art having a deep center of gravity; and posture at proper loft angle and lie angle with the sole surface in contact with the same ground as that where a ball sits.

In a design direction according to the related art (a direction of an arrow indicated by reference numeral 100 in FIG. 1), the idea of low gravity center and deep gravity center is kept held persistently, and as a result thereof, hitting a ball at a point off the center or off-center hitting becomes more conspicuous as the loft angle increases. In the invention, for the senior golfers and female golfers who have nothing to do with the increase in back spin and the trajectory in which the ball is blown up, the gravity center depth VZG does not have to be deepened, and hence, an opposite method (a direction indicated by reference character A in FIG. 1) of the one according to the related art is adopted in which the gravity center depth VZG is made shallow and the gravity center height at a lower location on the face surface 1 is lowered, so as to reduce the off-center amount. Since the gravity center depth VZG is made shallow and the gravity center height at the upper location on the face surface 1 is lowered, so as to reduce the off-center amount, the current state of the depth of the center of gravity is investigated, the results of which are shown in FIG. 2. It is indicated by a regression line that the gravity center depth (VZG) tends to increase by 0.7159 mm as the loft angle increases by one degree. Then, by attaching importance to this relationship and expecting an advantage that the height

FIG. 6 is a graph showing a relationship between the loft angle and the height of the center of gravity (HG).

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an embodiment of the invention will be described by reference the drawings.

FIG. 1 shows a wood golf club head in which a club head width (a depth from a leading edge 2 of a face surface 1 to a rearmost point of the club head) W is larger than a face maximum height H (refer to FIG. 3), and in the club head, a distance on a horizontal line from the leading edge 2 to the center of gravity G (a gravity center depth) VZG is designed as below:

VZG<0.7159×(loft angle)+11.78; and

VZG>face maximum height×tan(loft angle).

Besides, the depth (or the club head width) W is made to be 60 mm or more.

In addition, in order to attain the object of the invention, it is effective that a height HGR from a horizontal line which passes through a club head contact point to the center of gravity G is made to be low and the gravity center depth VZG is made to be shallow in such a state that a sole of the club head of the golf club is made to sit flat properly according the loft angle and the lie angle. The state in which the sole of the club head is made to sit flat properly means a state where the surface of the face of the club head is placed in an address of the center of gravity on the face surface 1 surely becomes lower than by the method according to the related art, the intercept of the function is determined so as to be lower than a golf club whose VZG is shallowest in the figure. The result is VZG<0.79159×(loft angle)+11.78 (equation 1).

By the use of the above equation 1, a club head (whose loft angle=26.3 degrees, VZG=33.1 mm, HGR=16 mm, roll radius=320 mm, face center height=15.7 mm) of a fairway wood is improved. From the equation 1, in the event that VZG is shallower than 30.6 mm, a club head results which is an improvement over the club head according to the related art in which the off-center amount is reduced. FIG. 3 shows the result of the improvement. By reducing the gravity center depth VZG of the club head according to the related art of 33.1 mm to 30.6 mm, the gravity center position on the face surface 1 is reduced by 1.1 mm, and the off-center mount is improved by 1.1 mm, leading to an increase in meet rate.

However, although the shallower the gravity center depth ZVG, the larger the advantage, when considering from the shape of the wood club head, a lower limit of the relation is the depth direction length of the face maximum height position of the club head according to the related art shown in FIG. 3, and in general, VZG>(face maximum height H)×tan(loft angle) (equation 2) is preferable.

The effect of modifying the curved shape of the face surface of the aforesaid club head according to the related art which is made up of the roll radius and the bulge radius into the cylindrical curved surface having only the bulge radius is studied using FIG. 4. Although the actual (real) loft angles of the club head according to the related art at the spot, face center and striking point are 8.5 degrees, 26.3 degrees and 25.4 degrees, respectively, due to the roll radius, by eliminating the roll radius, all the loft angles become the nominal loft angle (the loft angle at the face center) of the club head according to the related art of 26.3 degrees. Consequently, the loft angle at the striking point is changed from 25.4 degrees to 26.3 degrees, whereby the loft angle is increased by about 1 degree (actually. 0.9 degree). Consequently, the launch angle is increased, thereby making it possible to realize a trajectory having a high launch angle, which is advantageous to the senior golfers and female golfers. A bulge radius of the order of 10 inches, which is adopted in general, is adopted.

The roll radius denotes a radius of curvature of a portion extending from a boundary between the face surface 1 and a crown portion to the leading edge 2, and the bulge radius denotes a radius of curvature of a portion extending from a toe side to a heel side of the face surface 1.

As a club head construction in which the center of gravity G is made shallower and lower, measures can be adopted in which a weight is provided at a location on the sole portion which is closer to the face surface 1 or the rear of the crown portion is recessed to be lower than the other portions thereof.

In an exemplary embodiment of the invention, it is preferred that the loft angle is 15 degrees to 30 degrees. Further, it is preferred that the loft angle is 20 degrees or more for the average golfers, the senior golfers and the female golfers. Since the head speed of the golf club is slow when the average golfers, the senior golfers and the female golfers hit the ball, the back spin of the ball cannot be very effective in a lift force. Therefore, more preferably, the loft angle is set 25 degrees or more in order to the launch angle becomes higher. Besides, if the depth of the center of gravity is too shallow, the back spin of the ball is reduced. Therefore, it is preferred that the depth of the center of gravity VZG is 26 mm or more.

In an exemplary embodiment of the invention, the club head is formed by titanium alloy including a hollow portion, and the volume of the club head is 150 cc.

In an exemplary embodiment of the invention, it is preferred that the club head has the width W in the range 65 to 100 mm. 

1. A wood club head comprising: a face portion; and a sole portion, wherein: a distance between a point of intersection where a perpendicular which passes through the position of the center of gravity of the club head intersects a horizontal line which passes through a leading edge of the face portion in such a state that the sole portion of the club head sits flat properly and the leading edge, that is, a depth of the center of gravity VZG is defined as below: VZG<0.7159×(loft angle)+11.78; and VZG>face maximum height×tan(loft angle); a surface shape of the face portion is formed into a cylindrical curved surface having only a bulge radius; and a width of the club head, which is horizontal distance of the leading edge to the back end, is 65 mm or more and 100 mm or less. 